Radial piston pump

ABSTRACT

A pressure-limiting valve coaxial with the drive shaft is installed in a multi-piston pump. The valve is biased by a compression spring to closed condition to prevent output flow from the pump into a pressure-collecting dome of the housing. The spring is supported for reaction against a gasket having a throttle bore leading directly for flow toward a return chamber wherein the end of the pump shaft is a radial wall. When pressure in the pressure-collecting dome reaches a certain value, it will open the pressure-limiting valve against spring bias to relieve pressure through the throttle bore back into the suction channels of the pump. However, the relief flow through the throttle bore causes heating of the oil, an effect which is an important purpose of the invention on pump start-up. Thus, by making the return flow of reduced viscosity due to heating, such oil impinging against the shaft of the pump does not cause a sudden shift of the shaft against the pump housing. This reduces impact noises otherwise caused by cold oil of higher viscosity. Further, the positioning of the throttle bore directs the jet of oil into an axial bore in the drive shaft which oil subsequently is distributed to bearings which lubricates the shaft with warm, low viscosity oil.

BACKGROUND OF THE INVENTION

A radial multi-piston pump (DE-OS No. 35 22 796, for example) of thekind used herein has a pressure limiting valve that is coaxial with thedrive shaft and is accommodated in an intermediate cover. The pressurelimiting valve protects the pump and a consuming device connected withit against overloading after a maximum pressure determined by a springis reached. The upstream high-pressure side of the pressure limitingvalve is exposed to a collecting chamber that receives the oil underpressure from all pistons. The outlet side of the pressure limitingvalve is connected with a return chamber that is closed by the frontsurface of the drive shaft.

Impact noises develop when such a radial piston pump is cold started. Ifthe driver turns an auxiliary power steering mechanism supplied by thepump to highest pressure to get out of a parking space, the permissiblemaximum pressure builds up and the pessure limiting valve opens. Thislets the volume being delivered by the pump at the moment to flow backto the return chamber. A back pressure is developed in the returnchamber by the still viscous oil that, because of necessary shaft axialplay, suddenly moves the drive shaft against the pump casing. This isthe cause of the impact noises. The possibility of letting the oil flowoff to the suction side of the pump more quickly through several drilledholes, instead of only one, does exist. However, a resulting unfavorablecost of production results. Also, the oil mass that is present in theentire pump and in the suction line acts as retardant to flow. As aresult, the pump can only suck in a small volume initially when the oilis cold.

The objects of the invention are to eliminate the impact noises causedby a cold start; improve the pump's suction efficiency, improve thebearing lubrication efficiency while the pump is warming up by warmingthe return oil; maintain a low manufacturing cost, all effected by themain feature of the invention, viz., to warm return oil on start up.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the main feature of the invention, a throttle meansis installed downstream of the pressure limiting valve. In constructionthis throttle is a bore provided in a disc-like support which support isalready present as a reaction support for the compression spring of thepressure limiting valve.

The throttle converts the kinetic energy of the oil into heat energy asthe oil flows through the throttle to a return chamber so that the oil'sviscosity decreases. The oil flows from the return chamber more easily,so that the back pressure no longer suffices to impact against the driveshaft. Furthermore, the pump cylinders reach full volume more quickly,since the pistons suck in the warmer oil more rapidly. The warmer oilalso improves the bearing lubrication. The throttle provided in thespring support being merely a flow throttling bore provided therein hasno significant expense.

A detailed description of the invention now follows in conjunction withthe drawing in which:

FIG. 1 shows a radial piston pump in longitudinal section.

FIG. 2 shows an enlarged section of the pressure limiting valve andthrottling bore.

The radial piston pump has a housing 1, an intermediate cover 2, and adome 3 as a collecting chamber. A shaft 4 with an eccentric 5 operatesseveral pump pistons such as pistons 6 circumferentially arrangedradially to the axis of the shaft in the usual manner. The pistonsreciprocate in drilled cylinders 7. Screw caps 8 with guide bolts 10 forpressure springs 11 close the cylinders 7. The pressure springs 11 holdthe pistons 6 next to the surface of the circumference of the eccentric5. An oil tank (not shown) connects to a suction chamber 14 via asuction inlet 12 and a ring channel 13. The suction chamber 14 surroundsall the piston bases facing the eccentric 5. Each conveyor piston 6 hasfeed inlets 15 that act together with the suction chamber 14 in a knownmanner when the shaft 4 is rotating. During the compression stroke,interior spaces 16 in the pistons 6 are in turn connected with thecollecting chamber of the dome 3 through pressure ducts 17 and outletvalves 18. Dome 3 is connected with a consuming device (not shown)through a discharge outlet 19. A pressure limiting valve 20 coaxial withthe shaft 4 is installed in the intermediate cover 2. That valveprotects the pump and the consuming device against overloading. If thepressure in the dome 3 rises to a certain maximum value determined bythe closing bias of a spring 21 (FIG. 2), the ball 22 of 20 opens. Theoil can escape into the ring channel 13 through the hollow space 23(FIG. 2) around the spring and via a return chamber 24 (FIG. 1) and atransverse bore 25. The pistons then suck the oil into the cylindersagain. The shaft 4 supplies bearing means such as bearings 29 and 30with oil through an axial drilled bore 26 and radially drilled bores 27and 28.

The spring 21 is compressed against a gasket means such as a gasket 31for reaction support in a housing 32 of the pressure limiting valve. Inaccordance with the invention, the gasket 31 has a throttle bore 33which effects throttle means and which throttle bore is coaxial withbore 26. The throttle has a flow restriction effect operative to convertthe kinetic energy of the return oil to heat energy. Upon start up, coldoil pressure causes the pressure limiting valve to open and flow throughthe throttle causes a greatly heated jet of oil to flow directly intothe axial drilled hole 26 and to the bearings 29 and 30, in the criticalwarming-up phase. Thus, when the bearings are under the greatest stressthey are supplied with thinner lubricating oil. Due to a quicker heatingof the oil, an improved bearing lubrication and consequently good noisesuppression are also obtained. The warmer oil can flow back more quicklyinto the ring channel 13 from the return chamber 24 through thetransverse drilled hole 25 to enhance pump suction.

It will thus be apparent that the basic principle of the invention ascarried out in a simple change over the prior art brings about a vastimprovement in operation all as set forth hereinabove by operation of akinetic to heat conversion throttle.

I claim:
 1. In a multi-piston pump of the kind having a plurality ofradially arrayed pistons having means for actuation in sequential orderby a drive shaft (4) and including pressure limiting valve means (20)biased to closed position by spring means (21) wherein said pressurelimiting valve means is intermediate a pressure-collecting chamber means(3) and an end surface of the drive shaft; with return means (24, 25)for return flow to a suction inlet (12) of the pump upon opening of saidpressure limiting valve;the improvement comprising kinetic to heatenergy converting throttle means being disposed to throttle flow fromsaid pressure limiting valve means to said return means wherein saidflow impinges on said end surface of said drive shaft upon opening ofsuch pressure limiting valve means and wherein return flow through saidthrottle means of initially cold oil is thereby heated and rendered lessviscous for recirculating to said suction inlet of said pump and alsoreducing impact of return oil against the end of said drive shaft fornoise reduction in the operation of said pump.
 2. In a multi-piston pumpas set forth in claim 1, including support means (31) disposedintermediate said pressure limiting valve means and said end surface ofsaid drive shaft; said throttle means being bore means through saidsupport means,said spring means being held in compression by saidsupport means to bias closed said pressure limiting valve means.
 3. In amulti-piston pump as set forth in claim 1, including bearing meanscomprising bearings (29, 30) for said drive shaft and lubricating means(26, 27, 29) providing communication of heated return oil forlubricating said bearings.
 4. In a multi-piston pump as set forth inclaim 1, said throttle means comprising support means (31) disposedintermediate said pressure limiting valve means and said end surface ofsaid drive shaft; said throttle means being bore means through saidsupport means.
 5. In a multi-piston pump as set forth in claim 3, saidlubricating means comprising oil bores (26, 27, 28) in said drive shaftleading to said bearings and having communication with said throttlemeans.
 6. In a multi-piston pump as set forth in claim 5, at least onesaid oil bore (26) being exposed in relation to with said throttle meansto receive a direct jet therein of heated return oil from said throttlemeans.
 7. In a multi-piston pump as set forth in claim 6, said one oilbore being an axial bore (26) in said drive shaft; said lubricatingmeans including oil bores (27, 28) in said drive shaft communicatingbetween said axial bore and said bearing means; said throttle meanscomprising a coaxial throttle bore (33).
 8. In a multi-piston pump ofthe kind having a plurality of radially arrayed pistons having means foractuation in sequential order by a drive shaft (4) and including apressure limiting valve (2) biased to closed position by a spring (21)wherein said pressure limiting valve is intermediate a pressurecollecting chamber means (3) and an end surface of the drive shaft withreturn means (24, 25) for return flow to a suction inlet (12) of thepump upon opening of said pressure limiting valve;the improvementwherein means comprising a throttle (33) is disposed to throttle flowfrom said pressure limiting valve to said return means so that said flowimpinges on said end surface of said drive shaft upon opening of suchpressure limiting valve and whereby return flow through said throttle ofinitially cold oil is thereby heated and rendered less viscous forrecirculating to said suction inlet of said pump and also reducingimpact of return oil against the end of said drive shaft for noisereduction in the operation of said pump; wherein said throttle effects aflow restriction which converts the kinetic energy of return flow toheat energy.
 9. In a multi-piston pump of the kind having a plurality ofradially arrayed pistons having means for actuation in sequential orderby a drive shaft (4) and including a pressure limiting valve (20) biasedto closed position by a spring (21) wherein said pressure limiting valvereleases excess pressure oil to a return chamber (24) for receivingreturn flow to a suction inlet (12) of the pump upon opening of saidpressure limiting valve; said return chamber being closed by an end ofsaid drive shaft;the improvement comprising throttle means having athrottle bore (33) being disposed to throttle return flow from saidpressure limiting valve to said return chamber and operative to convertthe kinetic energy of said return flow to heat energy wherein said driveshaft has lubrication means comprising an axial open ended bore (26)coaxial with said throttle bore (33) disposed to directly receive returnflow therefrom for lubricant to said pump; said return flow impinges onsaid end surface of said drive shaft; whereby return flow through saidthrottle bore of initially cold oil is thereby heated and rendered lessviscous for recirculating to said suction inlet of said pump and forlubrication of said pump and also for reducing impact of return oilagainst the end of said drive shaft to reduce noise in the cold startoperation of said pump.